Electrostatic deflection electrode system for electron beam device having an array of lenses

ABSTRACT

ACCURATELY SPACED, PARALLEL CONDUCTORS FORMING AN ARRAY OF DEFLECTION ELECTRODES ARE PROVIDED TO RESPECTIVELY DEFLECT AN ELECTRON BEAM EMANATING FROM ONE OR MORE OF ANY ARRAY OF LENSES. THE ARRAY OF ELECTRODES ARE CONSTRUCTED BY FIRST FORMING A STACK OF PLANAR SHEETS COMPRISING ALTERNATE LAYERS OF THE ELECTRODE MATERIAL AND A SECOND REMOVABLE MATERIAL WHICH ACTS AS AN ACCURATE SPACER DURING FABRICATION OF THE ARRAY.

Nov. 30, 1971 w. L. JONES 3,623,197

ELECTROSTATIC DEFLECTION ELECTRODE SYSTEM FOR ELECTRON BEAM DEVICEHAVING AN ARRAY OF LENSES Filed March 27, 1970 2 Sheets-Sheet 1 "mm"F|vG.2.

FORMING AN ASSEMBLY OF F I6, I, [1'4 PLANAR LAYERS cou msme ALTERNATELAYERS 0F DISS/MILAR MATERIALS.

SLICING THE ASSEMBLY IN A PLANE NORMAL TO THE LAYERS.

SELECTIVELY REMOVING THE OTHER MATERIAL.

INVENTORZ WILLIAM L. JONES,

Nov. 30, 1971 w. L. JONES 3,623,197

' ELI'J'C'IROS'IATIC DEFLEC'I'ION ELECTRODE SYSTEM FOR ELECTRON BEAMDEVICE HAVING AN ARRAY 0F LENSES Filed March 27. 1970 2 Sheets-Sheet 8INVENTOR:

WILLIAM L. JONES M BY kl g HIS ATTORN Y.

United States Patent US. Cl. 2925.14 4 Claims ABSTRACT OF THE DISCLOSUREAccurately spaced, parallel conductors forming an array of deflectionelectrodes are provided to respectively deflect an electron beamemanating from one or more of an array of lenses. The array ofelectrodes are constructed by first forming a stack of planar sheetscomprising alternate layers of the electrode material and a secondremovable material which acts as an accurate spacer during fabricationof the array.

BACKGROUND OF THE INVENTION This invention relates to an electron beamtube having a compound lens system comprising a plurality of focusingand deflecting electrodes in a matrix for precise control of theelectron beam. More particularly, the invention relates to a method ofmaking an array of deflection electrodes for a compound lens system.

A system for precise control of an electron beam is described in a paperby S. P. Newberry entitled Problems of Microspace Information Storage,appearing in the Fourth Electron Beam Symposium (Mar. 29-30, 1962')published by Alloyd Electronics Corporation, Boston, Mass., and again inThe Flys Eye Lens-A Novel Electron Optical Component for Use With LargeCapacity Random Access Memories by S. P. Newberry in volume 29 of theAmerican Federation of Information Processing Societies, ConferenceProceedings, published by Spartan Books, Washington, DC. (November1966). The system therein described comprises an ultrahigh densitymemory wherein impingement of an electron beam on a storage medium iscontrolled by an objective lens made up of a matrix of minute electronoptical lenses, herein referred to as lenslets. This matrix of lensletsis superficially similar in appearance to the compound eye of anordinary housefly and therefore is designated a Flys Eye Lens. Byutilizing coarse deflection of the electron beam so as to strike only adesired lenslet of the matrix, the lenslet, thus struck, positions thebeam to ultimately impinge upon the storage medium at the desired point.Although the coarsely deflected beam may not strike the desired lensletat dead center, the accuracy with which the beam strikes the storagemedium remains unimpaired so long as even a portion of the beam strikesthe desired lenslet.

Briefly, the planar array of lenslets comprises three parallel plateswith a plurality of axially aligned openings therein to form an array ofEinzel lenses for fine focusing and, immediately following each lens, aset of X and Y deflection plates for fine deflection. The resultantultrahigh resolution electron beam tube can be used, for example, inapparatus for the fabrication of integrated circuits such as describedand claimed in US. Patent No. 3,491,236-Newberry, issued J an. 20, 1970and assigned to the assignee of this invention.

The X-Y deflection array comprises two sets of parallel deflection barsorthogonal to one another and electrically coupled respectively tohorizontal and vertical control circuitry. Alternate bars in each setare electrically coupled respectively to the positive and negative ofthe particular deflection circuit. Thus, the electron beam emanatingfrom any one or more of the Einzel lens passes through a pair ofhorzontal deflection bars and a pair of vertical deflection bars.

It has been proposed to construct such a deflection electrode array byindividually attaching accurately machined bars individually to aninsulating substrate. Problems such as inaccurate spacing, warpage dueto uneven heating, and overall time and expense have made this solutionundesirable.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide a method of making an accurately spaced deflection electrodearray. It is another object of this invention to provide a method ofmaking an array of parallel bars. Other objects of the invention willbecome apparent from the description.

Briefly considered, in accordance with the invention a deflectionelectrode array is constructed by forming an assembly of planar layerscomprising parallel alternate layers of at least two dissimilarmaterials. The layers are secured together and the assembly is thensliced in a plane normal to the planes of the layers while maintainingsecurement of the layers to one another. Selected end portions of one ofthe materials are secured to an insulating substrate and then the othermaterial is selectively removed to provide an assembly of equidistantand parallel spaced elements. A second assembly is similarly constructedand the two assemblies are mounted in parallel planes with the axis ofthe bars or elements of one assembly orthogonal to the axis of the barsof the other assembly to provide an array of X-Y deflection electrodes.

:BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration showingapparatus embodying the deflection electrode array produced by theinvention.

FIG. 2 is a flow sheet of the invention.

FIG. 3 is an isometric view of the multilayered intermediate productformed by the process of the invention. 3 FIG. 4 is an isometric view ofa sliced portion of FIG.

FIG. 5 is an isometric view of a portion of FIG. 4 after partialetching.

FIG. 6 is a top view of the sliced portion of FIG. 4 mounted to asupport.

FIG. 7 is an exploded view of a deflection electrode array formed by theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, adevice is generally illustrated in which the deflection electrode arrayformed by the invention may be used. A vacuum enclosure is generallyindicated at 2 wherein a beam 4 of charged particles such as an electronbeam produced by an electron emitting source 6 is controllably deflectedthru a compound lens system onto a target 20 such as a semiconductorwafer.

Beam 4 produced by electron source 6 passes through a beam limitingaperture 8 and is collimated by an electrostatic condenser lens 10. Thebeam is then coarsely deflected in the X and Y planes respectively, bydeflection plates 12a, 12b and 14a, 14b. The particular electron opticsused to direct the beam to each lenslet may, of course, be varied andoptimized using various structures and techniques forming no part of thepresent invention.

The compound lens structure is generally indicated at 30 in FIG. 1. Theelectrostatic focusing lens structure generally comprises three parallelplates 32, 34, and 36, each having an array of openings therethrough inaxial alignment to form an array of electrostatic lenses.

Immediately following the focusing lens array is the fine deflectionsystem toward which this invention is directed. Briefly, the deflectionsystem comprises a first set of parallel bars 60 immediately followed bya second set of parallel bars 90 at right angles to the first set ofbars. The bars thus form a criss-cross array of lattice conformingspacially to the openings in the lens plates to provide a fine X-Ydeflection system for each lens. Thus maintenance of even and parallelspacing of the deflection bars is desirable.

In accordance with the invention an array of parallel and evenly spaceddeflection bars is constructed following the steps outlined in the flowsheet of FIG. 2 by first forming an assembly such as illustrated in FIG.3 comprising alternate layers of at least two dissimilar materials. Thesheets or layers comprising one of the materials are indicated by thenumeral 66. This material is chosen for its removability at a laterstage of the fabrication as will be explained below. Its function is toact as a temporary thickness gauge and alignment device for correctspacing and parallel alignment of the adjacent layers which willeventually become the deflection electrodes. The thickness of the layers66 is therefore carefully selected to correspond to the desired eventualspacing between the electrodes of the desired deflection electrodearray.

Alternating with layers 66 are layers of the desired electrode materials62a, 64a, 62b, 64b, 62c, and 64c. It will be noted that the layersindicated by the numeral prefix 62 extend from one side of the stackwhile the layers indicated by the numeral prefix 64 extend out on theopposite side of the stack and also that these layers are staggered.This construction, as will be explained in more detail presently, ispreferred as an aid to eventual electrical interconnection of theelectrodes to provide alternate positive and negative deflection platesfor either the X or Y axis.

The thickness of the plates 62 and 64, i.e. the width of the bars, ischosen to correspond with the desired spacing between the electrodes andthe spacing of the lenslets in the Einzel lens array with which theeventual deflection electrode assembly is to operate. Other than forsuch design limitations the thickness of the plates 62 and 64 need onlyexceed the minimum necessary for mechanical stability of the particularelectrode material chosen.

In the preferred embodiment the electrode material comprising plates 62and 64 is titanium metal of about -30 mils thickness. Titanium electrodematerial is desirable because of its non-magnetic properties, itsbondability to ceramic insulating materials, its low emission, andgettering properties.

Nickel-plated molybdenum is a preferred material for layer 66 whentitanium electrode material is chosen. With this choice of materials theinitial assembly can be brazed together, followed by a second, lowertemperature braze of the titanium electrodes to a ceramic substrate suchas fosterite without disturbing the titanium-nickelmolybdenum braze.When other electrode materials are used or other securement of theelectrodes to a substrate utilized, the second material can of course beother than molybdenum.

The assembly of titanium and nickel coated molybdenum plate is securedtogether by vacuum brazing at about 1000 C. for about ten minutes. Thelength of brazing time will vary somewhat depending upon the thicknessof the nickel coating forming the Ti-Ni braze. A thickness of nickel ofabout /2 mil has been found to be satisfactory.

After the brazed assembly has been cooled, it is sliced normal to theplanes of the layers into portions 50 such as shown in FIG. 4 of about30 mils thickness. The sliced surfaces, if necessary, are ground flat toassure uniformity of thickness.

The sliced portion 50 (with all layers still brazed together) is thenmounted on a suitable support. In accordance with a preferred embodimentof the invention, portion 50 is mounted to a ceramic disk 100 which ispreferably fosterite ceramic. When the conducting layers are made oftitanium and the ceramic is fosterite, a very satisfactory bond can beeflected following the bonding method described and claimed in Beggs US.Patent 2,857,663, issued Oct. 28, 1958 and assigned to the assignee ofthis invention. Briefly, this patent teaches and claims the bonding oftitanium to fosterite by a titanium-nickel-active-alloy seal.

When the above bonding technique is used, the molybdenum layers arepreferably etched back from the ends of slice 50 as illustrated in FIG.5. The selective partial etching can be done by suitably masking thecentral portion of the slice to maintain the slice in one piece thuspreserving the alignment of the titanium layers. The etching can be doneusing an etching solution comprising 3 parts by weight water, 1 part byweight 12. N nitric acid, and 1 part by weight 12 N sulfuric acid. Afterthis etching step is done, the protruding titanium portions are nickelplated to provide a satisfactory amount of nickel to effect thenickel-titanium-fosterite bond taught by the above Beggs patent.

As best seen in FIG. 6, sliced portion 50 is bonded to a ceramic supporthaving a central cutaway portion of suflicient dimension to allow theshort ends 62d, 62e, 62f, and 64d, Me, and 64f to rest on disk 100.Subsequent bonding of the titanium bars 62 and 64 to disc 100' providesbonding of both ends of each bar to disc 100.

Still referring to FIG. 5, strips and 82 are illustrated as mounted ondisc in respective electrical contact with the longer ends 62a, 62b, 62cand 64a, 64b, and 64c. Strips 80 and 82 comprise thin nickel-titaniumfoil strips which are laid down on disc 100 before the slice comprisingbars 62 and 64 is bonded to disc 100. In this way, the subsequentbonding provides simultaneous mechanical adhesion of bars 62 and 64 todisc 100 and electrical interconnection of alternate titanium electrodebars.

It should be noted here that the etching back of the molybdenum layersadjacent the ends of the bars is done to inhibit undesiredinterconnection of adjacent bars which could occur if the slice was notseparated into discrete portions at the area of the bond.

After the subassembly or slice is brazed to the ceramic support, theremainder of the removable spacer layers illustrated herein asmolybdenum can be removed. In the case of molybdenum, this can be doneusing an etching solution comprising 3 parts by weight water, 1 part byWeight 12 N nitric acid, and 1 part by weight 12 N sulfuric acid. Thissolution will effectively remove the molybdenum without affecting eitherthe titanium layers or the titanium-nickel-fosterite seal.

The sealing technique described above provides the additional advantageof electrically interconnecting the protruding portions on each end ofthe subassembly. As mentioned above, these protruding layers arealternately spaced in the subassembly. Electrical interconnection of theprotruding portions then permits, after removal of the spacing layers,electrical connection of the bars to a power source to provide alternatepolarity on adjacent bars.

The deflection electrode assembly is completed .by the production of asecond subassembly 112 mounted to a similar ceramic substrate 110. Asshown in FIG. 7, the two mounted subassemblies 102 and 112 are mountedtogether with the respective bars orthogonal. A ceramic spacer insulatessubassembly 102 from subassembly 112. Electrical connection of therespective electrodes to X and Y deflection power sources provides anarray or lattice work of X+, X, Y+, and Y deflection electrodes todeflect the electron beam emanating from the corresponding lens in thepreceding lens array.

Alternatively, the array may be formed by mounting one of the slicedportions to one side of a ceramic spacer and mounting the other slicedportion to the opposite side of the spacer with the bars of onesubassembly orthogonal to the bars of the other subassembly. If closerspacing of the X-axis bars to the Y-axis bars is desired,

both sets of bars could be mounted on the same side of a ceramic spacerin a pair of grooves in the spacer machined at 90 to one another, one ofwhich would be deeper than the other groove by slightly more than theheight of the bars.

Thus the invention provides a method of making an array of deflectionelectrodes for a compound lens system wherein the individual electrodesare accurately spaced apart. The electrode array of the invention, itshould be noted, is useful not only in a compound lens system but inother applications as well, such as a grid system Where accurate spacingis required. While a particular embodiment has been described minormodifications will be apparent to those skilled in the art and should bedeemed to be within the scope of the invention defined in the appendedclaims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A method of making a deflection electrode array for a matrix ofelectron lenses comprising:

(a) forming an assembly of planar layers comprising alternate layers ofat least two dissimilar materials, one of which comprises a conductingmaterial,

(b) securing said layers together,

() slicing said assembly in a plane normal to the planes of the layerswhile maintaining securement of said layers to one another,

(d) securing together selected layer portions of said conductingmaterial at each end of said slice to a support, and

6 (e) thereafter selecting material other than said conductive materialto provide an array of equidistant and parallel spaced elements.

2. The method of claim 1 wherein said assembly comprises alternatelayers of titanium and molybdenum brazed together.

3. The method of claim 2 wherein said conducting material comprises saidtitanium layers, and said layers are secured by brazing said titanium toa ceramic support.

4. The method of claim 3 wherein the molybdenum layers at the endportions of said sliced assembly are selectively removed by chemicaletching before said titanium layers are brazed to said ceramic supportand the remainder of said molybdenum is removed by chemical etchingafter said titanium layers are brazed to said ceramic to insurealignment of said titanium layers.

References Cited UNITED STATES PATENTS 2,791,710 5/1957 Dressler29-25.14 X 2,857,663 10/1958 Beggs 29503 X 3,491,236 1/1970 Newberry29-580 X JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, AssistantExaminer US. Cl. X.R.

